This invention relates to an instrument and a method for measuring the resistance of the fastener members such as snap fasteners to plucking from the fabric of garments and the like to which they are attached.
Fastener members, such as snap fasteners each consisting of a female fastener member known as a socket and a male fastener member known as a stud (the two members for use as a combination being hereinafter called xe2x80x9cfastener membersxe2x80x9d) and fancy buttons, are in abundant use on garments and the like. Garment manufacturers today are required to assure certain pluck resistance of those fastener members as the Product Liability (PL) Act and regulations on small-size articles have come in force in the U.S. Of those fasteners, snap fasteners have a structure in which the male and female fastener members are resiliently engaged or disengaged, the members being attached opposite to each other to mate on overlapping edges of a garment fabric. Each fastener member is secured in place with a backing member known as a prong which consists of a flanged or annular base formed with several slender protrusions or prongs extending upright from the base. If a fastener member thus secured to the fabric comes off easily, an infant can swallow it or its backing member. To avoid this danger, each snap member or other similar fastener member must be guaranteed to resist plucking with forces at or beyond a predetermined level. For example, an official standard in Europe demands that a fastener pulled with a force of 90 N (newton) for 10 seconds should not come off the cloth to which it is secured. This standard has come to be accepted in this country too.
Inspection for pluck resistance, therefore, has become necessary at sewing factories. Now that the PL Act has been enforced in Japan too, testing of this character is imperative. Actually, however, the manufacturers are determining the pluck resistance by their own testing procedures, because the enforcement regulations do not stipulate the measuring method. Thus, much variation of the measured values presents a problem of the impossibility of proper evaluation.
We have already provided an instrument for measuring the pluck resistance of fasteners by Patent Application Kokai No. 9-37811. The instrument permits proper inspection with less variation than heretofore. The instrument (1) presses the fabric of a garment to which a fastener member (e.g., a socket or stud member of a snap fastener) has been attached with a prong or other backing member, securely around the fastener member; (2) while about the same time constrains the fastener member with forces exerted in the directions at right angles to the sides of the member; and (3) pulls the fastener member away in the direction at right angles to the surface of the fabric to which it is attached. To realize this sequence of steps, the instrument comprises means for pressing the fabric of a garment to which a fastener member is attached, securely around the member, means for constraining the sides of the socket member, tensile means for pulling the stud member away in the directions at right angles to the fabric surface to which the member is attached, and means for measuring the tensile force exercised by the tensile means.
For the measurement of pluck resistance there are two testing methods, destructive and non-destructive. Neither directly indicates the pluck resistance with individual garments to which test fastener members are attached. However, the measurement guarantees the pluck resistance of the fastener members made of the same material and by the same manufacturing steps. In the form of a nondestructive test, a fastener member may be pulled with a given (reference) tensile force, and if the member does not come off, then it is a concrete guarantee for the pluck resistance to plucking forces up to that limit. Conversely if the fastener is plucked off with forces below the limit, the test is destructive. The invention is thus applicable to the both tests, destructive and nondestructive. Moreover, the invention provides an instrument capable of testing, when desired, with tensile forces greater than the reference level.
The afore-described instrument has a disadvantage, however. Because its measuring means is designed to continuously indicate the numerical value of force, it is necessary to monitor constantly and determine pluck resistance and decide whether it is passable or not case by case. This presents little problem in sampling inspection but gives much inconvenience in total inspection where a large number of articles must at a time be inspected and judged whether they pass or not given tests.
The present invention is aimed at providing an instrument and a method for measuring snap resistance values of fastener members such as fastener members precisely, rapidly, and in a simple manner.
The aim of the invention is achieved by partial improvements in a measuring instrument as described in Japanese Patent Application Kokai No. 9-37811 (U.S. Pat. No. 5,798,767). Parts like those described in the above literature will be briefly outlined here and reference should be had to the literature for details.
The present invention provides a pluck-resistance measuring instrument for fastener members which comprises holder means for holding a fabric of a garment to which a fastener member is attached, securely around the fastener member, a plurality of clamp members capable of clamping the fastener member and moving in the direction normal to the surface of the fabric where the fastener member is attached to the fabric, and tension detector means for measuring the tensile force that is applied to the clamp members, wherein said holder means is supported by lift means, said tension detector means comprises a member providing a fulcrum, a mass lever pivotally supported at the fulcrum and a tension detector, said mass lever being coupled at one end to said clamp members and adapted to act on the tension detector at the other end.
In a preferred embodiment of the invention, the tension detector is set so that it can detect a reference value of predetermined tension.
While the reference value may be detected using an electric switch as the tension detector that supports the other end of the lever, the tension detector in a preferred embodiment of the invention is a load cell and the other end of the lever rests on the load cell, the fulcrum and the mass distribution of the lever being set so that when the reference value has been attained the other end of the lever comes away from the load cell to no load.
In this aspect the load cell may be designed to determine tensile force up to the reference value.
Another embodiment of the invention uses a second load cell, and the other end of the lever is located beneath, and away from, the second load cell to determine any force above the reference value.
The invention also provides a method for measuring the pluck resistance of fasteners using the above instrument, which method comprises the steps of (1) starting the lift means to lower the holder means, (2) judging whether the force on the tension detector is at or above the reference value or not, (3) judging, if the force is below the reference value, whether the holder means has reached the lower limit position or not and, if it has not yet reached the lower limit position, repeating the above step (2), (4) reporting that the test piece has passed the inspection if the reference value is reached or exceeded in the step (2), and reporting that the test piece has failed if the lower limit position is reached in the step (3).
The invention further provides a measuring method comprising the above steps which further comprises the step of moving the lift means backward after the step (4) or (5) and, when the holder means has been reset to the upper limit position, stopping the lift means.
Moreover, the invention provides a measuring method which comprises the steps of (1) starting the lift means to lower the holder means, (2) judging whether the force on the tension detector is at or above the reference value or not, (3) judging, if the force is below the reference value, whether the holder means has reached the lower limit position or not and, if it has not yet reached the lower limit position, repeating the above step (2), (4) starting timing if the reference value is reached or exceeded in the step (2), judging again whether the force on the tension detector is at or above the reference value or not, and, if the force is at or above the reference value, reporting that the test piece has passed the inspection when the timing has reached a reference time, and (5) reporting that the test piece has failed if the lower limit position is reached in the step (3).
The method further comprises the step of moving the lift means backward after the step (4), (5) or (6) and, when the holder means has been reset to the upper limit position, stopping the lift means.
Further, the invention may further comprise the step of stopping the lift in the step (4) and, if the force is below the reference value, starting again the lift in the step (1).